11. Have you seen the following creatures underwater?
Crab - everywhere.
Moray eel - near the trapped K8.
Shark - between Lambda and the CURIE.
Manta ray - at Delta.
Snail - at the floating spheres near Omicron.
Gulper eel - in the abyss, near the climber.
Shrimp - between Tau and Alpha.

12. There are two ways to enter the transit system: by freeing the K8, or by fiddling with a control panel.

13. In the shuttle, you can see slightly different videos by choosing different locations.

14. After the shuttle crash, if you forget the Omnitool and then go back for it, you have a super-cool encounter with a Flesher. (Credit to reddit.)

15. There's a sunken submarine called the Pequod.

16. If you get hurt by the Flesher at Lambda, the subsequent dialogue is slightly different.

17. If you enter the crashed shuttle before meeting Catherine, Simon mentions it while discussing the ARK.

18. If you sabotage the CURIE without talking to Catherine, she later freaks out. (Credit to reddit.)

22. In Catherine's room, you can pick up various objects to ask Catherine about them (a robot teddy, a Chinese fan, a doll, a piece of the Vivarium, and a proto-ARK). She also becomes more annoyed the longer you stay.

23. At the end of Theta's residential hallway, there's a locked door. If you look through the window, you can barely glimpse an enemy (either Akers or a Proxy - I'm not sure which).

The robot head girl says things like "Away", "Don't come any closer", etc. as the player moves in her area.

After entering Tau, you can hear "Caution, airlock pressurizing". When moving forward to the rooms located on the side further ahead, and then backtracking towards the entrance through the hallway, you can see the airlock door opening for Johan Ross.

I forgot some things about the K8, but #2 and #3 (below) may have been coincidences. They certainly seemed deliberate - can anyone confirm?

Spoiler below!

1. The K8 plays a little tune when it rescues you. I'm sure everyone noticed, but it was a great moment.
2. Soon after I freed it, the K8 stopped at a coral growth and shined its light on a small hole. When I looked closer, I saw a moray eel. I would have missed it otherwise.
3. At Delta, there's a station with broken K8s. As I poked around, the active K8 came over and nuzzled one of the broken ones. (Think WALL-E.) Then it came over and nuzzled me! Too cute.

1. In the beginning dream sequence, Ashley says that the red tracer fluid is green. This is a reference to the inverted spectrum thought experiment.

Pretty sure this is just in reference to the traffic light in the dream scenario you're. You can hear a bunch of cars honking and stuff right after she says it.

I always thought #6 was weird, the talking door in Upsilon. Never thought I'd feel weird about killing a metal door, but it was interesting. Cool list so far! A lot of these I encountered in my playthrough, but some of these are pretty neat.

You can choose to keep Amy alive in the transit station, only unplug one of the sockets then go back to the switchboard, activating it will give the message "emergency power only". The shuttle will still crash, but it will give the error message "power unstable" as opposed to the track blockage message.